JP5147292B2 - Surface-modified polyamide film and method for producing the same - Google Patents

Description

  The present invention relates to a surface-modified polyamide film and a method for producing the same, and more particularly to a polymer film surface-modified by corona discharge treatment and a method for producing the same.

  The polymer film is frequently printed with characters, pictures, etc. on its surface, and the surface printability is required. However, in general, the surface of a polymer film often exhibits water repellency. Therefore, the surface of the polymer film is modified by surface treatment.

  Conventional surface treatment methods for polymer films include methods for imparting hydrophilicity to the surface and improving printability by discharge treatment such as plasma discharge treatment and corona discharge treatment, and flame treatment. Or the method etc. which form the chemical | medical agent film | membrane which has a hydrophilic group on the film surface are mentioned. Among these, plasma discharge treatment and corona discharge treatment are industrially useful and widely used because of their high processing speed and high effect.

  However, in the conventional corona discharge treatment, minute processing unevenness occurs, and there is a problem that printing omission occurs in recent semi-tone printing under severe conditions.

  As a method for uniformly surface-treating a polyamide film, Patent Documents 1 to 3 propose performing plasma discharge treatment and corona discharge treatment. Patent Document 1 discloses a corona discharge method in which an insulating coating layer containing a high dielectric constant material is formed on the surface of an earth roll for conveying a web or a metal roll of a roll electrode so that the web is uniformly charged. It is disclosed. In Patent Document 2, the surface of the polymer film is subjected to a discharge treatment such as corona discharge treatment or plasma discharge treatment, and then at least the surface subjected to the discharge treatment is brought into contact with water or a water-soluble liquid. By performing the surface treatment, it has been disclosed to impart high hydrophilicity to the film surface and to reduce the decrease in hydrophilicity over time. Further, Patent Document 3 discloses a surface pretreatment process in which a continuous film sheet is subjected to corona discharge treatment or atmospheric pressure plasma discharge treatment, and a main surface treatment in which the film sheet is subjected to atmospheric pressure plasma discharge treatment in succession to the surface pretreatment process. And a method for introducing a desired functional group uniformly and reliably.

However, if the web is charged with a high electric field strength and the charge amount is made uniform, the absolute value of the charge amount of the web becomes large, and there is a problem that electrostatic disturbances such as blocking and sparking easily occur. Further, the method of contacting with water or an aqueous solution is disadvantageous industrially because the apparatus becomes complicated. Furthermore, the plasma discharge treatment has a drawback that it is difficult to handle compared to the corona discharge treatment. Thus, a simple and uniform surface modification method that can be applied to semi-tone printing under severe conditions in recent years has not been proposed.
JP 58-4157 A JP 7-330930 A JP 2000-80184 A

  The present invention solves the above-mentioned problems, and is a method for surface treatment of a polyamide film. It is an object of the present invention to provide a surface-modified polyamide film obtained by the method.

  As a result of extensive research, the present inventor conducted corona discharge treatment on the polyamide film with a weak electric field intensity to suppress the occurrence of electrostatic disturbances such as blocking and sparks, and further, twice or more with the weak electric field intensity. By performing a large number of corona discharge treatments, it becomes possible to perform uniform corona discharge treatment on the entire film without any minute processing unevenness, and furthermore, polyamide having uniform wettability over a small range of the treated surface and the entire treated surface The inventors have found that a film can be obtained and have reached the present invention.

That is, the gist of the present invention is as follows.
(1) A polyamide film that has been subjected to corona discharge treatment and has been surface-modified, wherein the polyamide film is passed through a corona discharge field comprising a discharge electrode and a counter electrode roll twice or more times, Two or more corona discharge treatments were performed, and the corona discharge was generated by a high voltage electric field having an average electric field strength of 1 to 50 kV / cm, and measured at intervals of 10 cm in the width direction of the polyamide film. Taking a point, the maximum value when the contact angle of the polyamide film with respect to water is measured at 10 measurement points at 2 mm intervals in the width direction of the polyamide film with the measurement point as the center, θ1max, the minimum value is θ1min, The average value is θ1av, the maximum value of θ1av at all measurement points is θ2max, and the minimum value is θ2 When the in, the following in all of the measurement points (Equation 1) and a polyamide film (Formula 2) was filled and was surface-modified and satisfies the following (Equation 3).

θ1max−θ1min ≦ 5 deg. (Formula 1)
45 deg. ≦ θ1av ≦ 55 deg. (Formula 2)
θ2max−θ2min ≦ 5 deg. (Formula 3)

(2) Measurement points are taken at 10 cm intervals in the width direction of the polyamide film, and the contact angle of the polyamide film with water is measured at 10 measurement points at intervals of 2 mm in the width direction of the polyamide film with the measurement point as the center. When the maximum value is θ1max, the minimum value is θ1min, the average value is θ1av, the maximum value of θ1av at all measurement points is θ2max, and the minimum value is θ2min, the following (formula In producing a surface-modified polyamide film characterized by satisfying 1) and (Formula 2) and satisfying the following (Formula 3), a corona discharge field composed of a discharge electrode and a counter electrode roll is subjected to 2 times or it than is often times passes, and facilities to corona discharge treatment of 2 times or more, corona A method for producing a surface-modified polyamide film, characterized in that the discharge is generated by a high voltage electric field having an average electric field strength of 1 to 50 kV / cm .
θ1max−θ1min ≦ 5 deg. (Formula 1)
45 deg. ≦ θ1av ≦ 55 deg. (Formula 2)
θ2max−θ2min ≦ 5 deg. (Formula 3)

  According to the method of the present invention, when modifying the surface of a polyamide film, it is simple and hardly causes electrostatic damage, and it is possible to perform a uniform corona discharge treatment on the entire film without causing minute processing unevenness. Furthermore, by the surface treatment, it is possible to obtain a polyamide film having uniform wettability over a small range of the treated surface and the entire treated surface.

  In the present invention, measurement points are taken at 10 cm intervals in the width direction of the surface-modified polyamide film, and the contact angle of the polyamide film with respect to water is set at 10 points at intervals of 2 mm in the width direction of the polyamide film centering on the measurement points. The maximum value when measured at the measurement point is θ1max, the minimum value is θ1min, the average value is θ1av, and the maximum value of θ1av at all measurement points is θ2max and the minimum value is θ2min. It is necessary to satisfy the following (formula 1) and (formula 2) and satisfy the following (formula 3).

θ1max−θ1min ≦ 5 deg. (Formula 1)
45 deg. ≦ θ1av ≦ 55 deg. (Formula 2)
θ2max−θ2min ≦ 5 deg. (Formula 3)

  Regarding Equation 1, preferably θ1max−θ1min ≦ 3 deg. And more preferably θ1max−θ1min ≦ 2 deg. It is. When there is a measurement point satisfying θ1max−θ1min> 5 deg., processing unevenness occurs in a minute range on the surface of the film that has been surface-modified.

  For Equation 2, preferably 45 deg. ≦ θ1av ≦ 50 deg. And more preferably 45 deg. ≦ θ1av ≦ 48 deg. It is. θ1av <45 deg. In this case, since the degree of treatment on the film surface is too strong, there is a risk of causing static electricity damage such as blocking or sparking. θ1av> 55 deg. In this case, the film surface is insufficiently processed, the wettability is low, and there is a possibility that a problem may occur in printing.

  Regarding Equation 3, preferably θ2max−θ2min ≦ 3 deg. And more preferably θ2max−θ2min ≦ 2 deg. It is. If θ2max−θ2min> 5 deg., processing unevenness occurs on the entire surface of the surface-modified film, and thus there is a risk of uneven printing density.

  Furthermore, if the average value of θ1av for all measurement points is θ2av, it is inevitably 45 deg. ≦ θ2av ≦ 55 deg. It becomes. In this case, the processing degree in the whole film is appropriate. Preferably 45 deg. ≦ θ2av ≦ 49 deg. And more preferably 45 deg. ≦ θ2av ≦ 48 deg. It is.

  One embodiment of a corona discharge treatment apparatus according to the present invention is shown in FIG. Here, 1 and 2 are high-voltage power supplies, 3 and 4 are discharge electrodes, 5 and 6 are counter electrode rolls, and 7 is a guide roll. 8 is a polyamide film to be subjected to corona discharge treatment. As for any member, those of a known corona discharge treatment apparatus can be basically used.

  In the production method of the present invention, it is necessary to perform the corona discharge treatment twice or more times on the polyamide film. It is preferable to carry out twice or three times. Even if the corona discharge treatment is performed four or more times, the effect of surface modification of the film is saturated and hardly changed, and the apparatus becomes large. In the corona discharge treatment, it is difficult to generate a completely uniform corona discharge even if the discharge needles in the discharge electrode are installed at a high density. Prone to occur.

  The corona discharge device used in the present invention may have a form having two or more discharge electrodes 3, 4 as shown in the figure, preferably a form having two or three, or a discharge The form which has 2 or more apparatuses, Preferably the form which has 2 or 3 units | sets may be sufficient.

  In the present invention, for all corona discharge treatments, it is preferable to set the average electric field strength represented by the applied voltage of corona discharge / distance between electrodes to 1 to 50 kV / cm. More preferably, it is 20-40 kV / cm. When the average electric field strength is less than 1 kV / cm, effective corona discharge hardly occurs and the surface treatment effect becomes poor. On the other hand, when the average electric field strength exceeds 50 kV / cm, electrostatic disturbances such as blocking and sparking tend to occur.

  In the present invention, the polyamide film is preferably a film mainly composed of the following polyamide resin. That is, as the polyamide resin, a polyamide resin obtained by polycondensation such as a lactam having three or more members, a polymerizable ω-amino acid, a dibasic acid and a diamine can be used. Specifically, polymers such as ε-caprolactam, aminocaproic acid, enanthractam, 7-aminoheptanoic acid, 11-aminoundecanoic acid, 9-aminononanoic acid, α-pyrrolidone, α-piperidone; hexamethylenediamine, nona Polycondensation of diamines such as methylenediamine, undecamethylenediamine, dodecamethylenediamine, and metaxylylenediamine with dicarboxylic acids such as terephthalic acid, isophthalic acid, adipic acid, sebacic acid, dodecanedioic acid, and glutaric acid Examples thereof include polymers obtained by caulking, and copolymers thereof. For example, nylon 4, 6, 7, 8, 11, 12, 6 · 6, 6 · 10, 6 · 11, 6 · 12, 6T, 6/6 · 6, 6/12, 6 / 6T, 6I / 6T Etc. From the viewpoint of excellent mechanical properties and thermal properties, it is preferable to use nylon 6 as a main component, particularly when used for packaging.

  Furthermore, various additives and modifiers that are usually blended as necessary, for example, lubricants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, antistatic agents, tackifiers, seals A property improver, an antifogging agent, a crystal nucleating agent, a mold release agent, a plasticizer, a crosslinking agent, a flame retardant, and a colorant (pigment, dye, etc.) may be added.

  In the present invention, the polyamide film for performing corona treatment for the purpose of surface modification can be produced by a known production method. For example, after extruding a molten polymer from a T-die, it is cooled with a casting roll to produce an unstretched sheet, which is simultaneously biaxially stretched or sequentially biaxially stretched. The stretched film is subjected to a short heat treatment at a temperature of around 200 ° C. in order to improve dimensional stability.

  After this heat treatment, corona treatment is preferably performed in a process until the polyamide film is wound up. Or it is also possible to give a corona treatment in the slit process implemented while winding up once and winding up. Corona treatment can be applied in both steps.

  In addition, in order to impart functionality to the film, an anti-strength agent, an adhesion improving composition, and a barrier resin are applied to an unstretched polyamide film using an in-line coat stretching technique as long as the surface treatment is not affected. It is also possible to stretch the film after coating.

  The polyamide film may be a single layer film or a coextruded laminated film if the surface layer is polyamide.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples without departing from the gist thereof. In addition, each physical property of the film was calculated | required by the method shown below.

  (1) Contact angle: Measured according to the sessile drop method described in JIS R3257. However, the measurement location was as follows. That is, for a polyamide film having a width of 4 m, a total of 39 measurement points were taken at 10 cm intervals in the width direction from the end of the film along the width direction, and for each measurement point, the contact angle of the surface modified surface with water Was measured at 10 points at 2 mm intervals in the width direction of the film with the measurement point as the center. The maximum value of the contact angle measured at 10 measurement points was θ1max, the minimum value was θ1min, and the average value was θ1av. Further, the maximum value of θ1av for 39 measurement points was θ2max, and the minimum value was θ2min.

  (2) Wetting tension: measured according to JIS K6768.

(3) Semi-tone printability: Observed printing loss occurring on the surface of a film printed with a gravure roll (screen 150 lines × 30 μm × 30%) using a light scope at an area of 27 cm ² at a magnification of 30 times. Thus, the number of pieces per 1 cm ² was determined. The evaluation criteria were as follows.

◎: 1cm white dots per ² 0-1 ○: 1cm white dots per ² 2-5 △: 1cm ² per print missing number of 6 to 10 ×: Printing per 1cm ² missing More than 10

Example 1
A nylon 6 raw material containing 0.2% by mass of silica particles having an average particle diameter of 1.5 μm and 0.05% by mass of ethylene bisstearamide as an additive was prepared, and melt-extruded using an extruder and a T-die. This was wound around a casting drum and solidified by cooling to produce an unstretched sheet. This unstretched sheet was sent to a hot water tank whose temperature was adjusted to 70 ° C., and subjected to a humidity conditioning treatment for 1 minute. Then, the sheet end along the width direction is held by a clip of a flat simultaneous biaxial stretching machine, and simultaneously biaxially stretched at a stretching ratio of 3.0 times in length and 3.3 times in width at 195 ° C. gave. Subsequently, the transverse relaxation rate was set to 5%, heat treatment was performed at 200 ° C. for 3 seconds, and a biaxially stretched polyamide film original having a width of 4 m and a thickness of 15 μm was obtained through a cooling process. The original film is supplied to the corona discharge treatment apparatus shown in FIG. 1, is brought into close contact with the counter rolls 5 and 6, and is passed through the corona discharge field of the discharge electrodes 3 and 4. Corona discharge treatment was performed. At this time, the average electric field strength was 15 kV / cm, and the film running speed was 50 m / min.

  Table 1 shows the water contact angle, wetting tension, and halftone printability of the treated surface of the obtained polyamide film. In Table 1, regarding the value of θ1max−θ1min and the value of θ1av, the range from the minimum value to the maximum value for the 39 measurement points described above is described.

Examples 2-4 and Comparative Examples 1-5
Compared to Example 1, the number of corona treatments and the average electric field strength were changed. Other than that was carried out similarly to Example 1, and obtained the surface-modified polyamide film. The measurement results for the obtained film are shown in Table 1. In addition, when the frequency | count of the corona discharge process was 1 time, the corona discharge process was performed without using the discharge electrode 4 in FIG. When the number of times of corona discharge treatment was 3, after treatment twice as in Example 1, the corona discharge treatment was performed one more time without using the discharge electrode 4.

  According to the measurement results shown in Table 1, the difference between θ1max and θ1min was reduced by performing the corona discharge treatment a plurality of times. This indicates that there is little processing unevenness in the minute range. Looking at the evaluation of the wetting tension, almost no difference is observed in any of the conditions, and thus it can be seen that the conventional wetting tension evaluation is insufficient for the evaluation of processing unevenness in this minute range.

  For θ1av, the corona treatment was performed a plurality of times, and the difference (θ2max−θ2min) between the minimum value (θ2min) of θ1av and the maximum value (θ2max) was reduced. From this, it was found that, by performing the treatment a plurality of times as compared with the case where the corona discharge treatment is performed only once, a more uniform surface modification can be performed on the entire film.

  That is, all of Examples 1 to 4 satisfied (Expression 1) and (Expression 2) at all measurement points, and also satisfied (Expression 3). On the other hand, in Comparative Example 1 to Comparative Example 5, unlike those of Examples 1 to 4, the (Equation 1) and (Equation 2) are satisfied at all measurement points, and (Equation 3) is satisfied. There was nothing to satisfy.

  In Comparative Example 5, the corona discharge treatment was performed only once, but blocking occurred due to the influence of the average electric field strength being too high, and the halftone printability could not be evaluated.

It is a figure which shows the one aspect | mode of the corona discharge processing apparatus concerning this invention.

Explanation of symbols

1, 2 High voltage power supply 3, 4 Discharge electrode 5, 6 Counter electrode roll 7 Guide roll 8 Polyamide film

Claims (2)

A polyamide film subjected to corona discharge treatment and surface-modified,
The polyamide film is subjected to corona discharge treatment twice or more times by passing it twice or more times through a corona discharge field comprising a discharge electrode and a counter electrode roll,
The corona discharge is generated by a high voltage electric field having an average electric field strength of 1 to 50 kV / cm,
When measuring points are taken at intervals of 10 cm in the width direction of the polyamide film, and the contact angle of the polyamide film with respect to water is measured at 10 measuring points at intervals of 2 mm in the width direction of the polyamide film with the measurement point as the center. When the maximum value is θ1max, the minimum value is θ1min, the average value is θ1av, and the maximum value of θ1av at all measurement points is θ2max and the minimum value is θ2min, the following (Equation 1) and A surface-modified polyamide film characterized by satisfying (Expression 2) and satisfying (Expression 3) below.
θ1max−θ1min ≦ 5 deg. (Formula 1)
45 deg. ≦ θ1av ≦ 55 deg. (Formula 2)
θ2max−θ2min ≦ 5 deg. (Formula 3) When measuring points are taken at intervals of 10 cm in the width direction of the polyamide film, and the contact angle of the polyamide film with respect to water is measured at 10 measuring points at intervals of 2 mm in the width direction of the polyamide film with the measurement point as the center. When the maximum value is θ1max, the minimum value is θ1min, the average value is θ1av, and the maximum value of θ1av at all measurement points is θ2max and the minimum value is θ2min, the following (Equation 1) and In producing a surface-modified polyamide film characterized by satisfying (Formula 2) and satisfying the following (Formula 3) :
Corona discharge field consisting of the discharge electrode and the counter electrode roll, twice or it than is often times passes, and facilities to corona discharge treatment of 2 times or more,
A method for producing a surface-modified polyamide film, wherein the corona discharge is generated by a high voltage electric field having an average electric field strength of 1 to 50 kV / cm .
θ1max−θ1min ≦ 5 deg. (Formula 1)
45 deg. ≦ θ1av ≦ 55 deg. (Formula 2)
θ2max−θ2min ≦ 5 deg. (Formula 3)

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